Flowering tops of Hypericum perforatum contain a number of classes of structurally different substances that act directly or indirectly on the central nervous system. The mechanisms of action of these compounds are different and comprise anti-MAO action (Suzuki O R. et al. Planta Med., 272-4, 1984), action on serotonin release and re-uptake (Muller W. E. et al Pharmacopsychiatry, 30, 102-107, 1997) and benzodiazepine-like activity (Coot J. M. Pharmacopsychiatry 30,108-112, 1997).
Hyperforin, a floroglucin derivative, is one of the main components of the lipophilic fraction of Hypericum perforatum flowering tops; said fraction also contains adhyperforin, a hyperforin higher homologue, although in lower concentration (Erdelmeier C. A. J., Pharmacopsychiatry, 31, 2-6, 1998).

Hyperforin has recently been the object of numerous studies that establish its important role as an antidepressant (Pharmacopsychiatry, 31 Suppl. 1, 1-60. 1998). Furthermore, it is recognized that the extracts of Hypericum perforatum can be used for the prophylaxis and treatment of neurodegenerative diseases, inter alia Alzheimer's disease (WO/9940905, WO0057707). In particular, hyperforin and adhyperforin salts with inorganic cations or ammonium salts were described for this purpose (WO9941220).
It is known from literature that hyperforin is poorly stable in the usual extraction and storage conditions; according to WO 97/13489, the hyperforin content in a St. John's Wort water-alcoholic extract falls already after a few weeks. WO 97/13489 further recites that, in order to obtain hyperforin stable extracts, antioxidants should be present during the whole work up (extraction, purification and storage). It is therefore evident that the high instability of hyperforin makes the preparation of hyperforin pharmaceutical formulations quite difficult. In order to obviate to said drawback, compounds more stable than hyperforin, such as the salts disclosed in WO 99/41220 and the hydroxy-functionalized derivatives (WO 99/64388) cited above, have recently been prepared.
It is moreover known (Bystrov et al., Bioorg. Khim, 1978) that hyperforin and adhyperforin can be transformed into the corresponding octahydroderivatives, octahydrohyperforin (Ia) and octahydroadhyperforin (Ib), by catalytic reduction of the isoprene side chains

or into the corresponding tetrahydroderivatives, tetrahydrohyperforin (Ic) and tetrahydroadhyperforin (Id), by reduction of the keto groups at the 1- and 10-positions to hydroxy groups with metal hydrides.
